What is the status of the gas flow?
The gas flow rate was re-set to the "nominal" value of 4 cc/min, in mid-March 1992. There had been problems seen with small pulses toward the middle of 1991. One response was to lower the operating HV from 3060 to 3000volts. The other response was to use tank A (instead of tank B, the "proper" tank for PSPC-B), and increase the flow rate slightly (the flow rate was 6 cc/min at the end of September 1991). A problem with the regulating valve in January 1992 caused the "click-rate" to be lowered (which does not affect the gas flow rate). By the end of February 1992, tank A was empty, and MPE started using the gas from tank C. Since everything has been behaving nicely, the flow rate was reduced to 4 cc/min, and that's the way things have been running since (Message from U. Briel to R. Harnden). The PSPC gas supply was virtually exhausted by January of 1994, and the HRI was moved into the focal plane for the rest of the missions pointed observations. A small amount of PSPC gas remains in the tank for a few final calibration observations, and in case of any urgent targets of opportunity.
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